JP5915269B2 - Start control device for compression self-ignition engine - Google Patents

Description

  The present invention is provided in a vehicle equipped with a compression self-ignition engine that burns fuel injected into a cylinder from a fuel injection valve by self-ignition, and automatically stops the engine when a predetermined automatic stop condition is satisfied. And a start control device that restarts the engine by injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor when a predetermined restart condition is established. .

Compressed self-ignition engines such as diesel engines are generally more widely used as in-vehicle engines in recent years because they are more thermally efficient than spark ignition engines such as gasoline engines and emit less CO ₂ I am doing.

In the compression self-ignition engine as described above, in order to further reduce CO ₂ , the engine is automatically stopped at the time of idle operation or the like, and then the engine is restarted when the vehicle is started. It is effective to adopt a so-called idle stop control technique, and various studies have been conducted on this.

  As an example, Patent Document 1 below discloses that a diesel engine is stopped when a predetermined automatic stop condition is satisfied, and then a fuel injection is performed while driving a starter motor when a predetermined restart condition is satisfied. A control device for a diesel engine that restarts the engine is disclosed.

  Specifically, in this document, when the diesel engine is automatically stopped, the stop position of the piston of the stop-time compression stroke cylinder in the compression stroke at that time is examined. After that, when the engine restart condition is satisfied, it is determined whether or not the piston stop position of the compression stroke cylinder at the time of stop is in an appropriate position set relatively near the bottom dead center. The first fuel is injected into the stop compression stroke cylinder, and the combustion is restarted from the first compression that reaches the first compression top dead center as a whole, whereby the engine is restarted (hereinafter, This is called “1 compression start”). On the other hand, when the piston stop position in the compression stroke at the time of stop is on the top dead center side from the appropriate position, the cylinder that has been stopped in the intake stroke (intake stroke cylinder at the time of stop) shifts to the compression stroke. The first fuel is injected into the cylinder, and the engine is restarted by resuming combustion from the second compression which reaches the second compression top dead center as a whole (hereinafter referred to as “two-compression start”). ).

JP 2009-62960 A

  In the technique of the above-mentioned patent document 1, when the piston of the compression stroke cylinder at the time of stoppage is in the proper position, the engine can be restarted quickly by one compression start, but when it has deviated from the proper position to the top dead center side. Requires a two-compression start, which increases the time required for restart. That is, in the two-compression start, since the fuel is injected after waiting for the intake stroke cylinder at the time of stoppage to enter the compression stroke, the energy from the combustion can be used until the second compression is reached after the first compression. This is not possible, and the restart time is increased accordingly. For this reason, it has been desired to enable engine restart by one compression start as frequently as possible.

  By the way, in order to increase the frequency of the one-compression start, it is necessary to improve the ignitability of the fuel injected into the compression cylinder at the time of stop. For this purpose, it is effective to promote atomization of the fuel. In order to promote atomization of the fuel, the fuel pressure of the fuel injection valve (the pressure of the fuel supplied to the fuel injection valve) may be increased. However, after the engine is completely stopped by the automatic stop control, the fuel injection valve Since the supply pump that supplies fuel (generally operating with the driving force of the engine) is also stopped, it is impossible to increase the fuel pressure. Of course, if the supply pump is replaced with an electric one, the supply pump can be driven even when the engine is stopped, but this increases the cost.

  Therefore, when a general supply pump driven by the engine is used, the control for increasing the fuel pressure needs to be completed before the engine is completely stopped. At this time, if the highest priority is given to the improvement of fuel consumption, the control for increasing the fuel pressure is performed during the period in which the engine is rotating by inertia after execution of fuel cut (control to stop fuel injection from the fuel injection valve). In addition, it is desirable to use the driving force of the engine that is rotating in inertia. However, since the period during which the engine rotates by inertia is not so long, even if an attempt is made to increase the fuel pressure during this inertia rotation period, the fuel pressure may not reach the target value in some cases.

  The present invention has been made in view of the circumstances as described above, and at the time of automatic engine stop, the fuel pressure is increased by using as much as possible the period during which the engine is inertially rotated. It is an object of the present invention to provide a start-up control device for a compression self-ignition engine that can increase the opportunity for quick restart by one compression start while minimizing to a minimum.

In order to solve the above problems, the present invention is provided in a vehicle equipped with a compression self-ignition engine that burns fuel injected from a fuel injection valve into a cylinder by self-ignition, and has a predetermined automatic stop condition. By automatically stopping the engine when established, and then injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor when a predetermined restart condition is established, A start control device for restarting the engine, a fuel cut control means for executing a fuel cut to stop fuel injection from the fuel injection valve when the automatic stop condition is satisfied, and an inertia of the engine after the fuel cut Detecting means for detecting a predetermined parameter proportional to the compression top dead center pressure in the cylinder when rotating at From as fuel pressure above Symbol fuel injection valve until the engine stops completely rises to a predetermined target value, and the fuel pressure adjusting means for starting the fuel pressure increase control at a predetermined timing after establishment of the automatic stop condition Determining means for determining whether or not the piston of the compression stroke cylinder at the time of stoppage in the compression stroke when the engine is completely stopped is in a specific range set on the bottom dead center side from a predetermined reference stop position; When it is determined that the piston of the stop compression stroke cylinder has stopped within the specific range and the engine restart condition is satisfied, the fuel injection valve is controlled to control the first fuel in the stop compression stroke cylinder. The fuel injection valve receives fuel from a supply pump mechanically driven by an engine, and the fuel cut control means The fuel cut timing in relation to the fuel pressure increase control is variably set according to the parameter value detected by the detection means, and the fuel cut timing set by the fuel cut control means is When the parameter is higher than a predetermined value, the timing is set to be later than the start point of the fuel pressure increase control. On the other hand, when the parameter is equal to or lower than the predetermined value, The fuel cut is set earlier than the fuel cut timing when the fuel pressure is high, and earlier than the fuel pressure rises to the target value (claim 1).

  In the present invention, “detecting a predetermined parameter proportional to the compression top dead center pressure” means not only the case where a physical quantity different from the compression top dead center pressure is detected, but also the compression top dead center pressure directly. This includes the case of detection.

  According to the present invention, since the fuel pressure increase control for increasing the fuel pressure of the fuel injection valve is executed after the automatic stop condition is satisfied until the engine is completely stopped, the engine is restarted after that. When fuel is injected from the fuel injection valve, the fuel can be atomized by a relatively high fuel pressure, and the ignitability of the fuel can be improved. When the ignitability of the fuel is enhanced, the piston stop position range (specific range) in which the compression start can be restarted by restarting the engine by fuel injection into the stop compression stroke cylinder can be expanded to the top dead center side. The opportunity for compression start can be increased to ensure quick startability. Moreover, since the fuel pressure increase control is executed before the engine is completely stopped, a general mechanical pump (a pump mechanically driven by the engine) is used as a supply pump for supplying fuel to the fuel injection valve. The fuel pressure can be raised properly.

In particular, in the present invention, when the detected parameter is higher than a predetermined value, the fuel cut is executed at a timing later than the start of the fuel pressure increase control (that is, after the actual fuel pressure has increased to some extent). When the above parameter is high, the pressure at the compression top dead center of each cylinder when the engine is rotating by inertia increases, so the resistance applied to the engine increases correspondingly, and the period of inertia rotation of the engine (fuel The period from the cut to the complete stop of the engine) is shortened. On the other hand, in the present invention, when the parameter is high, the fuel cut timing is delayed with respect to the fuel pressure increase control, so that the fuel pressure is increased with a margin even in a situation where the period of inertial rotation of the engine is relatively short. It is possible to ensure that the fuel pressure reaches a predetermined target value before the engine is completely stopped.

On the other hand, when the parameter is less than or equal to the predetermined value, the fuel cut timing is advanced compared to when the parameter is higher than the predetermined value, so that the low parameter leads to prolonged inertial rotation of the engine. Thus, the fuel pressure can be increased efficiently while suppressing fuel consumption. That is, if the above parameter is low (and therefore the compression top dead center pressure is low) , the resistance due to the compressed air during inertial rotation of the engine becomes small, and the period of inertial rotation of the engine after fuel cut becomes long. Therefore, in order to increase the fuel pressure by utilizing the force of the engine during inertial rotation, in the present invention, the timing of the fuel cut when the parameter is low is advanced, and at least before the completion of the fuel pressure increase control (the fuel pressure is the target Before the value is reached). As a result, the fuel pressure can surely reach the target value while avoiding deterioration in fuel consumption due to consumption of extra fuel.

  As described above, according to the present invention, when the engine is automatically stopped, the fuel pressure can be increased by utilizing the inertial rotation period as much as possible, so that one compression is performed while minimizing the influence on fuel consumption. The opportunity for quick restart by starting can be further increased.

  In the present invention, preferably, when the fuel cut timing set by the fuel cut control means is higher than the predetermined value, the parameter falls within a range later than the start time of the fuel pressure increase control. The higher the value, the slower the parameter is set. On the other hand, when the parameter is less than or equal to the predetermined value, the parameter is set at the same time as the start of the fuel pressure increase control.

As described above, when the fuel cut timing in relation to the fuel pressure increase control is set to be slower as the above parameter is higher, the greater the resistance during inertial rotation of the engine, the longer the delay from the start of the fuel pressure increase control. Thus, the fuel cut is executed, and the desired increase in fuel pressure can be reliably obtained even if the inertial rotation period is considerably short.

Further, when the above parameter is equal to or less than a predetermined value, the fuel cut is executed at the same time as the start of the fuel pressure increase control. Therefore, as compared with the case where the fuel cut is waited for a while after the start of the fuel pressure increase control. Thus, the fuel cut timing can be further advanced, and the fuel consumption at the time of automatic stop can be further reduced. Moreover, even if the fuel cut is executed simultaneously with the start of the fuel pressure increase control, the inertial rotation period of the engine is prolonged due to the low parameter , so that the fuel pressure is sufficiently increased by using the engine rotational force during that period. Can be raised.

  In the present invention, preferably, the parameter detected by the detecting means is atmospheric pressure.

  According to this configuration, for example, the structure for parameter detection can be further simplified as compared with a case where the compression top dead center pressure during inertial rotation is directly detected by the in-cylinder pressure sensor.

  In the present invention, preferably, the injection control means, after the restart condition is satisfied, at least as the first fuel injection to the compression stroke cylinder at the time of stop, the peak of the heat generation rate is passed after the compression top dead center. The main injection that causes the main combustion to greet and the pre-injection that causes the pre-combustion to reach the peak of the heat generation rate before the start of the main injection are executed (Claim 4).

  In this configuration, after the engine is automatically stopped, pre-injection is first executed at the time of one compression start in which the engine is restarted by fuel injection into the stop-time compression stroke cylinder, and then main injection is executed. The pre-injected fuel is combusted by self-ignition after a predetermined ignition delay (pre-combustion), and increases the in-cylinder temperature and pressure of the compression stroke cylinder at the time of stop, so when main injection is subsequently executed, The injected fuel will burn soon by self-ignition (main combustion). Thus, since the ignitability of the fuel injected by the main injection is improved by the pre-injection (pre-combustion) before that, even if the compression allowance in the stop compression stroke cylinder is not so much, the stop compression stroke cylinder Combustion at is ensured. As a result, the piston stop position range (specific range) in which one compression start is possible can be expanded to the top dead center side, and the engine start can be further accelerated.

  The compression self-ignition engine may be a diesel engine having a geometric compression ratio set to less than 16. (Claim 5)

  A diesel engine having a geometric compression ratio of less than 16 has a compression ratio lower than that of a diesel engine that has been widely used so far, and a compression allowance by a piston that stops in the middle of the compression stroke (compression from the piston stop position). Since there are many cases where the stroke amount to the top dead center is not sufficiently secured, the ignitability at the time of restart is relatively deteriorated. Therefore, the configuration of the present invention that improves the ignitability at the time of restart by increasing the fuel pressure can be suitably applied to a diesel engine having a geometric compression ratio of less than 16.

  The compression self-ignition engine may have a crankshaft connected to an automatic transmission via a torque converter.

In an AT vehicle equipped with a torque converter and an automatic transmission, a period during which the engine rotates by inertia after a fuel cut is shorter than an MT vehicle equipped with a clutch and a manual transmission. For this reason, the configuration of the present invention in which the fuel cut timing is delayed when the parameter is high is suitably applied to the AT vehicle rather than the MT vehicle.

  As described above, according to the start-up control device for a compression self-ignition engine of the present invention, when the engine is automatically stopped, the fuel pressure is increased by utilizing the period during which the engine is inertially rotated as much as possible. It is possible to increase the chances of quick restart by one compression start while minimizing the impact on the engine.

It is a figure showing the whole diesel engine composition to which the starting control device concerning one embodiment of the present invention was applied. It is a figure which shows schematic structure of the power train system containing the said engine. It is a system diagram which shows schematic structure of the fuel supply system of the said engine. It is a flowchart which shows the specific procedure of the automatic stop control of the said engine. It is a time chart which shows the change of each state quantity at the time of the automatic stop control of the engine. It is a figure which shows the map used in order to determine the timing of the fuel cut performed at the time of the said engine automatic stop control. It is a figure for demonstrating the time relationship between a fuel cut and fuel pressure raise control. It is a flowchart which shows the specific procedure of the restart control of the said engine. It is a figure for demonstrating the reference | standard stop position of the compression stroke cylinder at the time of a stop. It is a figure which shows what timing the fuel based on each injection burns when pre-injection and main injection are performed. It is a figure for demonstrating the modification of this invention.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of a diesel engine to which a start control device according to an embodiment of the present invention is applied. The diesel engine shown in the figure is a four-cycle diesel engine mounted on a vehicle as a power source for driving driving. The engine body 1 of this engine is of a so-called in-line 4-cylinder type, and includes a cylinder block 3 having four cylinders 2A to 2D (see also FIG. 2 to be described later) arranged in a row in a direction orthogonal to the paper surface, and a cylinder. It has a cylinder head 4 provided on the upper surface of the block 3 and a piston 5 inserted into each of the cylinders 2A to 2D so as to be able to reciprocate.

  A combustion chamber 6 is formed above the piston 5, and light oil as fuel is supplied to the combustion chamber 6 by injection from a fuel injection valve 15 described later. The injected fuel (light oil) is self-ignited in the combustion chamber 6 that has been heated to a high temperature and pressure by the compression action of the piston 5 (compression self-ignition), and the piston 5 pushed down by the expansion force due to the combustion is moved vertically. It is designed to reciprocate.

  The piston 5 is connected to the crankshaft 7 via a connecting rod (not shown), and the crankshaft 7 rotates around the central axis in accordance with the reciprocating motion (vertical motion) of the piston 5. .

  FIG. 2 is a diagram simply showing a powertrain system including the engine body 1. As shown in FIG. 2, the crankshaft 7 of the engine body 1 is connected to the automatic transmission 101 via a torque converter 102. That is, the vehicle on which the diesel engine of this embodiment is mounted is an AT vehicle in which a speed change operation is automatically performed.

  The torque converter 102 includes a pump impeller that rotates integrally with the crankshaft 7 of the engine body 1, a turbine runner that is disposed opposite to the pump impeller, and a stator that is disposed between the pump impeller and the turbine runner. It has a conventionally known structure. The rotation of the pump impeller is transmitted to the turbine runner via the working fluid (ATF oil) in the torque converter 102 and finally extracted as the rotation of the input shaft 103 of the automatic transmission 101. The automatic transmission 101 has a conventionally well-known structure including a meteor gear mechanism and a frictional engagement element (clutch or brake), and the speed of the vehicle is controlled by hydraulically controlling the intermittent engagement of the frictional engagement element. A desired shift speed (for example, one of six forward speeds or one reverse speed) is realized.

  Returning to FIG. 1 again, the configuration of the diesel engine of the present embodiment will be described. In the four-cycle four-cylinder diesel engine as in the present embodiment, the pistons 5 provided in the cylinders 2A to 2D move up and down with a phase difference of 180 ° (180 ° CA) in crank angle. For this reason, the timing of combustion (fuel injection therefor) in each of the cylinders 2A to 2D is set to a timing shifted in phase by 180 ° CA. Specifically, if the cylinder numbers of the cylinders 2A, 2B, 2C, and 2D are 1, 2, 3, and 4, respectively, the first cylinder 2A → the third cylinder 2C → the fourth cylinder 2D → the second cylinder Combustion is performed in the order of 2B. Therefore, for example, if the first cylinder 2A is in the expansion stroke, the third cylinder 2C, the fourth cylinder 2D, and the second cylinder 2B are respectively in the compression stroke, the intake stroke, and the exhaust stroke (see also FIG. 5 described later). ).

  The cylinder head 4 is provided with an intake port 9 and an exhaust port 10 that open to the combustion chambers 6 of the cylinders 2A to 2D, and an intake valve 11 and an exhaust valve 12 that open and close the ports 9 and 10, respectively. The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts and the like disposed in the cylinder head 4.

  The cylinder head 4 is provided with one fuel injection valve 15 for each of the cylinders 2A to 2D. Each fuel injection valve 15 is a multi-hole type having a plurality of injection holes (for example, 8 to 12) at the tip, and a fuel passage leading to each of the injection holes and a fuel passage are provided in the inside thereof. It has a needle-like valve element that is electromagnetically driven to open and close (both not shown). Then, the valve body is driven in the opening direction by electromagnetic force generated by energization, so that fuel supplied at a high pressure from a common rail 40 (accumulation chamber), which will be described later, is directly injected toward the combustion chamber 6 from each of the nozzle holes. It has become so.

  A cavity 5a is formed in the center portion of the crown surface (upper surface) of the piston 5 facing the fuel injection valve 15 so as to be recessed below other portions (peripheral edge portions of the crown surface). For this reason, when the fuel is injected from the fuel injection valve 15 with the piston 5 being near the top dead center, the fuel first enters the cavity 5a.

  Here, the engine body 1 of the present embodiment has a geometric compression ratio (ratio of the combustion chamber volume when the piston 5 is at bottom dead center and the combustion chamber volume when the piston 5 is at top dead center). Is set to 14. That is, the geometric compression ratio of a general vehicle-mounted diesel engine is often set to 18 or more, whereas in this embodiment, the geometric compression ratio is set to a considerably low value of 14. Has been.

  A water jacket (not shown) through which cooling water flows is provided inside the cylinder block 3 and the cylinder head 4, and a water temperature sensor SW1 for detecting the temperature of the cooling water in the water jacket is provided in the cylinder. It is provided in the block 3.

  The cylinder block 3 is provided with a crank angle sensor SW2 for detecting the rotation angle and rotation speed of the crankshaft 7. The crank angle sensor SW2 outputs a pulse signal in accordance with the rotation of the crank plate 25 that rotates integrally with the crankshaft 7, and based on this pulse signal, the rotation angle (crank angle) of the crankshaft 7 and The rotational speed (engine rotational speed) is detected.

  On the other hand, the cylinder head 4 is provided with a cam angle sensor SW3 for outputting cylinder discrimination information. That is, the cam angle sensor SW3 outputs a pulse signal according to the passage of the teeth of the signal plate that rotates integrally with the camshaft. Based on this signal and the pulse signal from the crank angle sensor SW2, Which cylinder is in which stroke is determined.

  An intake passage 28 and an exhaust passage 29 are connected to the intake port 9 and the exhaust port 10, respectively. That is, intake air (fresh air) from the outside is supplied to the combustion chamber 6 through the intake passage 28 and exhaust gas (combustion gas) generated in the combustion chamber 6 is discharged to the outside through the exhaust passage 29. It is like that.

  Of the intake passage 28, a range from the engine body 1 to the upstream side by a predetermined distance is a branch passage portion 28a branched for each of the cylinders 2A to 2D, and the upstream end of each branch passage portion 28a is a surge tank 28b. It is connected to the. A common passage portion 28c including a single passage is provided on the upstream side of the surge tank 28b.

  The common passage portion 28c is provided with an intake throttle valve 30 for adjusting the amount of air (intake flow rate) flowing into the cylinders 2A to 2D. The intake throttle valve 30 is basically fully opened during operation of the engine or maintained at a high opening degree close thereto, and is configured to be closed only when necessary, such as when the engine is stopped, to block the intake passage 28. Has been.

  An alternator 32 is connected to the crankshaft 7 via a belt or the like. This alternator 32 incorporates a regulator circuit that controls the current of a field coil (not shown) and adjusts the amount of power generation. Based on the current), the driving force is obtained from the crankshaft 7 to generate power.

  The cylinder block 3 is provided with a starter motor 34 for starting the engine. The starter motor 34 has a motor body 34a and a pinion gear 34b that is rotationally driven by the motor body 34a. The pinion gear 34b meshes with a ring gear 35 connected to one end of the crankshaft 7 so as to be detachable. When the engine is started using the starter motor 34, the pinion gear 34b moves to a predetermined meshing position and meshes with the ring gear 35, and the rotational force of the pinion gear 34b is transmitted to the ring gear 35. As a result, the crankshaft 7 is driven to rotate.

  FIG. 3 is a system diagram showing a schematic configuration of a fuel supply system for supplying fuel to the fuel injection valve 15. As shown in FIG. 3 (partially as shown in FIG. 1), the fuel supply system of the engine of this embodiment includes a fuel tank 40 for storing fuel (light oil), a fuel tank 40, Connected via a fuel pipe 41, a supply pump 43 that pumps up the fuel in the fuel tank 40 and sends it to a high pressure state, and a fuel pump 41 that is provided in the middle of the fuel pipe 41 while heating the fuel pumped up from the fuel tank 40 A fuel filter 42 for filtering, a fuel supply pipe 44 through which fuel pumped from the supply pump 43 passes, a single common rail (accumulation chamber) 45 connected to the downstream end of the fuel supply pipe 44, a common rail 45, A plurality of (four) branch pipes 46 connecting the fuel injection valves 15 of the cylinders 2A to 2D and the pressure (fuel pressure) of the fuel stored in the common rail 45 are below a predetermined value. The fuel and pressure limiter 47 that discharges from the common rail 45 includes a return pipe 48 for returning fuel discharged from the common rail 45 to the fuel tank 40 through the pressure limiter 47 when it becomes.

  The supply pump 43 is a mechanical plunger pump that operates with the driving force of the engine. Specifically, the input shaft 43a of the supply pump 43 is connected to the camshaft of the engine body 1 via a belt or a gear mechanism. When the input shaft 43a rotates in conjunction with the camshaft, the plunger built in the supply pump 43 reciprocates, and fuel is pumped from the supply pump 43 according to the reciprocation. ing.

  In addition, the supply pump 43 allows a part of the fuel pushed out by the plunger to escape to the return pipe 48 through the regulator pipe 50, so that the pressure of the fuel pumped from the supply pump 43 toward the common rail 45 is within a certain range. A suction control valve 43b (hereinafter abbreviated as “SCV”) for adjusting to the above is incorporated.

  An injector return pipe 49 is connected to the fuel injection valve 15 of each of the cylinders 2 </ b> A to 2 </ b> D to return the remaining fuel that has not been injected to the fuel tank 40. The downstream end of the injector return pipe 49 is connected to the regulator pipe 50, and the fuel discharged through the injector return pipe 49 is returned to the fuel tank 40 through the regulator pipe 50 and the return pipe 48. .

  A check valve 55 is provided in the middle of the injector return pipe 49. The check valve 55 has a function of keeping the pressure in the injector return pipe 49 constant by opening when the pressure of the fuel on the upstream side exceeds a predetermined value.

  The common rail 45 is provided with a fuel pressure sensor SW4 for detecting the pressure (fuel pressure) of the fuel stored therein. In addition, since the pressure in the common rail 45 is the same as the pressure of the fuel supplied to the fuel injection valve 15, the pressure detected by the fuel pressure sensor SW4 is referred to as “the fuel pressure of the fuel injection valve 15” below. Also called.

(2) Control system The engine configured as described above is centrally controlled by an ECU (engine control unit) 60 at each part. As is well known, the ECU 60 is a microprocessor including a CPU, a ROM, a RAM, and the like, and corresponds to a control unit according to the present invention.

  Various information is input to the ECU 60 from various sensors. That is, the ECU 60 is electrically connected to the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, and the fuel pressure sensor SW4 provided in each part of the engine, and input signals from these sensors SW1 to SW4. Based on the above, various information such as engine coolant temperature, crank angle, rotation speed, cylinder discrimination information, fuel pressure, and the like are acquired.

  The ECU 60 also receives information from various sensors (SW5 to SW10) provided in the vehicle. That is, the vehicle includes a vehicle speed sensor SW5 for detecting the traveling speed (vehicle speed) of the vehicle, an accelerator opening sensor SW6 for detecting the opening of the accelerator pedal 36 that is depressed by the driver, and a brake pedal. Brake sensor SW7 for detecting ON / OFF (presence / absence of brake) 37, atmospheric pressure sensor SW8 for detecting atmospheric pressure (pressure of outside air), and remaining capacity of a battery (not shown) Battery sensor SW9 and a room temperature sensor SW10 for detecting the temperature in the passenger compartment. Based on the input signals from these sensors SW5 to SW10, the ECU 60 acquires information such as the vehicle speed, the accelerator opening, the presence / absence of the brake, the atmospheric pressure, the remaining battery capacity, and the vehicle interior temperature. In the present embodiment, the atmospheric pressure sensor SW8 corresponds to detection means according to the present invention (means for detecting a predetermined parameter proportional to the compression top dead center pressure).

  The ECU 60 controls each part of the engine while executing various calculations and the like based on input signals from the sensors SW1 to SW10. That is, the ECU 60 is electrically connected to the fuel injection valve 15, the intake throttle valve 30, the alternator 32, the starter motor 34, the SCV 43b, and the like, and is driven by these devices based on the result of the above calculation and the like. Output control signal.

  More specific functions of the ECU 60 will be described. For example, during normal operation of the engine, the ECU 60 controls the SCV 43b and the like to maintain the fuel pressure of the fuel injection valve 15 at a desired value, or controls the fuel injection valve 15 to fuel the required amount of fuel according to the operating conditions. In addition to having a function of performing basic control such as injecting from the injection valve 15 or generating the required amount of electric power according to the electric load of the vehicle, the remaining capacity of the battery, etc. by controlling the alternator 32, so-called As an idle stop function, it also has a function of automatically stopping or restarting the engine under a predetermined specific condition. For this reason, the ECU 60 includes an automatic stop control unit 61 and a restart control unit 62 as functional elements relating to the automatic stop or restart control of the engine.

  That is, the automatic stop control unit 61 determines whether or not a predetermined automatic engine stop condition is satisfied during engine operation, and executes control to automatically stop the engine when it is satisfied. It is.

  The restart control unit 62 determines whether or not a predetermined restart condition is satisfied after the engine is automatically stopped, and executes control for restarting the engine when the restart condition is satisfied. is there.

(3) Automatic Stop Control Next, the contents of the automatic engine stop control executed by the automatic stop control unit 61 of the ECU 60 will be specifically described with reference to the flowchart of FIG. 4 and the time chart of FIG. As will be apparent from the description here, in this embodiment, the automatic stop control unit 61 of the ECU 60 serves as a fuel cut control means for executing a fuel cut for stopping fuel injection from the fuel injection valve 15. The function also serves as a fuel pressure adjusting means for increasing the fuel pressure of the fuel injection valve 15.

  When the processing shown in the flowchart of FIG. 4 is started, the automatic stop control unit 61 executes control for reading various sensor values (step S1). Specifically, the water temperature sensor SW1, the crank angle sensor SW2, the cam angle sensor SW3, the fuel pressure sensor SW4, the vehicle speed sensor SW5, the accelerator opening sensor SW6, the brake sensor SW7, the atmospheric pressure sensor SW8, the battery sensor SW9, and the room temperature sensor SW10. From each of these detection signals, based on these signals, engine coolant temperature, crank angle, rotation speed, cylinder discrimination information, fuel pressure, vehicle speed, accelerator opening, presence of brake, atmospheric pressure, remaining battery capacity, Acquire various information such as passenger compartment temperature.

  Next, the automatic stop control unit 61 determines whether or not an automatic engine stop condition is satisfied based on the information acquired in Step S1 (Step S2). For example, the vehicle is in a stopped state, the opening degree of the accelerator pedal 36 is zero (accelerator OFF), the brake pedal 37 is depressed more than a predetermined depression force (brake ON), and the engine coolant temperature is It is above a predetermined value (that is, warm-up has progressed to some extent), the remaining capacity of the battery is above a predetermined value, and the load on the air conditioner (the difference between the cabin temperature and the set temperature of the air conditioner) is relatively small It is determined that the automatic stop condition is satisfied when all of the plurality of requirements such as the above are met. As for the requirement that the vehicle is in a stopped state, it is not always necessary to make a complete stop (vehicle speed = 0 km / h), and the vehicle stops when the vehicle speed falls below a predetermined low vehicle speed (for example, 3 km / less). You may determine with being in a state.

  When it is determined YES in step S2 and it is confirmed that the automatic stop condition is satisfied, the automatic stop control unit 61 sets the opening degree of the intake throttle valve 30 to the normal opening degree (set during idle operation). For example, the control is performed to decrease from 80% to fully closed (0%) (step S3). In the time chart of FIG. 5, the time point when the automatic stop condition is satisfied is t0, and the time point after which the opening degree of the intake throttle valve 30 starts to be lowered is t1.

  Next, the automatic stop control unit 61 sets an initial value of an F / C start counter N for determining the start timing of a fuel cut (steps S10 and S11) described later based on the atmospheric pressure acquired in step S1. The control to perform is executed (step S4).

  In the present embodiment, the initial value of the F / C start counter N is set based on the map of FIG. According to the map of FIG. 6, the initial value of the F / C start counter N is set to 0 when the atmospheric pressure is lower than AP1 (for example, 75 kPa) or less, while when the atmospheric pressure is higher than AP1, the atmospheric pressure is As it rises, it is gradually increased to 1, 2, 3. When the atmospheric pressure exceeds AP2 (for example, 100 kPa), the initial value of the F / C start counter N is set to a maximum of 5. In addition, as a situation where atmospheric pressure becomes low, for example, when the vehicle is traveling in a high altitude with high altitude is considered.

  When the F / C start counter N is set as described above, the automatic stop control unit 61 determines whether or not the set value of the F / C start counter N is 0 (step S5).

  If it is determined NO in step S5, that is, if the initial value of the F / C start counter N is other than 0 (any one of 1 to 5) because the atmospheric pressure is higher than AP1, the automatic stop control unit 61 starts fuel pressure increase control for increasing the fuel pressure of the fuel injection valve 15 (step S6).

  Specifically, in the fuel pressure increase control in step S6, the target fuel pressure of the fuel injection valve 15 is increased from FP1, which is the target value during idling (before the start of automatic stop control), to FP2, which is higher by a predetermined amount. Then, as the target fuel pressure increases, the SCV 43b built in the supply pump 43 is fully closed. When the SCV 43b is fully closed, the flow of fuel that escapes from the supply pump 43 to the return pipe 48 through the regulator pipe 50 (broken arrow in FIG. 2) is cut off, and all the fuel from the supply pump 43 is supplied to the common rail 45. As a result, the pressure in the common rail 45 gradually increases. Then, by continuing such valve closing control of the SCV 43b for a predetermined period, the fuel pressure (actual fuel pressure) of the fuel injection valve 15 rises from FP1 to FP2. Note that the range of increase from FP1 to FP2 is, for example, 10 to several tens of MPa.

  In the time chart of FIG. 5, the target fuel pressure of the fuel injection valve 15 is set to increase and the fuel pressure increase control is started at a time t2 slightly delayed from the time t1 at which the intake throttle valve 30 starts to close. Then, after this time t2, the actual fuel pressure (actual fuel pressure) of the fuel injection valve 15 gradually increases and finally reaches the target value FP2.

  When the fuel pressure increase control is started as described above, the automatic stop control unit 61 determines whether or not the piston 5 of any cylinder of the engine body 1 has exceeded the top dead center (TDC) (step S7). ). Then, if it is determined as YES here and it is confirmed that the top dead center has been exceeded, an operation of subtracting 1 from the F / C start counter N is executed (step S8). That is, the value of the F / C start counter N is reset as N-1 which is smaller by 1.

  Next, the automatic stop control unit 61 determines whether or not the F / C start counter N is 0 (step S9). Then, when it is determined as YES and it is confirmed that N = 0, a fuel cut for stopping the fuel injection from the fuel injection valve 15 is executed (step S10). That is, the fuel injection is executed by setting the target injection amount, which is the amount of fuel to be injected from the fuel injection valves 15 of each cylinder 2A to 2D, to zero and stopping the fuel injection from all the fuel injection valves 15. To do.

  On the other hand, if it is determined NO in step S9, that is, if the F / C start counter N ≠ 0, the process returns to the above-described step S7 and subsequent steps, and any cylinder of the engine body 1 is in the up position. Every time the dead point is exceeded, the F / C start counter N is decremented by one. Then, the fuel cut is executed when N = 0 is reduced (step S10).

  As is apparent from such a control procedure, in the flowchart of FIG. 4, the timing of fuel cut (step S10) is variably set according to the initial value of the F / C start counter N set in step S4. . The fuel cut timing at step S10 is the earliest when the initial value of the F / C start counter N is 1. If the initial value of N is 1, only one of the cylinders of the engine body 1 exceeds the top dead center once, N = 0, and the fuel cut is executed. On the other hand, when the initial value of the F / C start counter N is 5, which is the maximum, the fuel cut timing is the latest. That is, since the fuel cut is not executed until any cylinder of the engine body 1 exceeds the top dead center five times, the fuel cut timing is delayed by four passes through the top dead center than in the case of N = 1.

  In the time chart of FIG. 5, as a case where the fuel cut timing is the latest, the target injection amount of the fuel injection valve 15 set when the initial value of the F / C start counter N is 5 is indicated by a solid line. . In this example of N = 5, the fuel cut is awaited from the time t2 (at the start of fuel pressure increase control) when the target fuel pressure of the fuel injection valve 15 is set to rise until the top dead center is exceeded five times. The fuel cut timing (timing at which the target injection amount is set to zero) is delayed, and is set to a time point t3 that is almost simultaneously with the actual fuel pressure (actual fuel pressure) of the fuel injection valve 15 reaching the target value FP2. I understand that

  After the fuel cut is performed, the engine temporarily rotates by inertia as shown by the engine speed waveform (solid line) after time t3 in FIG. Specifically, the engine rotational speed drops temporarily every time one of the four cylinders 2A to 2D reaches the compression top dead center (the top dead center between the compression stroke and the expansion stroke), and the compression top dead center is reduced. After going up and down, it will gradually decrease while repeating up and down.

  The time point t4 in FIG. 5 shows the timing of the final TDC, which is the top dead center that the engine finally reaches during the stop operation. After exceeding this final TDC, the engine never stops exceeding the top dead center (while temporarily rotating backward due to the swinging back of the piston) and reaches a complete stop at time t5. In FIG. 5, the cycle of each cylinder 2A to 2D when the engine is stopped (cylinder cycle after time t4 of the final TDC) is the expansion stroke of the first cylinder 2A, the compression stroke of the third cylinder 2C, and the fourth cylinder 2D. Is the intake stroke, and the second cylinder 2B is the exhaust stroke.

  After executing the fuel cut in step S10, the automatic stop control unit 61 determines whether or not the engine speed is 0 rpm, that is, whether or not the engine is completely stopped (step S13). When it is determined YES here and it is confirmed that the engine is completely stopped, the automatic stop control unit 61 sets the opening of the intake throttle valve 30 to the normal opening (for example, 80%). After returning (step S14), the automatic stop control is terminated.

Next, when it is determined YES in step S5, that is, since the atmospheric pressure is AP1 (for example, 75 kPa) or less, the initial value of the F / C start counter N set based on the map of FIG. The control in this case will be described. In this case, the automatic stop control unit 61 executes a fuel cut for stopping the fuel injection from the fuel injection valve 15 (step S11) and starts a fuel pressure increase control for increasing the fuel pressure of the fuel injection valve 15 (step S12). ). That is, when the initial value of the F / C start counter N is 0 (when the atmospheric pressure is AP1 or less), steps S6 to S10 executed when the initial value of N is other than 0 (1 to 5). Unlike the above, the execution of the fuel cut and the start of the fuel pressure increase control are set at the same time.

  In the time chart of FIG. 5, the target injection amount of the fuel injection valve 15 in the case where the initial value of the F / C start counter N is 0 is indicated by a broken line. In this example of N = 0, the target injection amount of the fuel injection valve 15 is set to zero at the same time t2 (at the start of fuel pressure increase control) when the target fuel pressure of the fuel injection valve 15 is set to increase, and the fuel cut is performed. You can see that it is running.

  When the fuel cut and the fuel pressure increase control are completed as described above, the automatic stop control unit 61 waits for the engine to completely stop (step S13), and then opens the opening of the intake throttle valve 30 at the normal time. The control to return to normal is executed (step S14).

  When the engine is completely stopped by the automatic stop control, the fuel pressure of the fuel injection valve 15 gradually decreases with time as shown in the rightmost part of the “actual fuel pressure” waveform in FIG. As the engine stops, the supply pump 43 mechanically driven by the engine also stops, and fuel is not supplied to the common rail 45. On the other hand, the common rail 45 is externally supplied little by little through a pressure limiter 47 and the like. This is because the fuel leaks.

Here, as described above, the initial value of the F / C start counter N set based on the atmospheric pressure is large as the timing relationship between the fuel pressure increase control for increasing the fuel pressure and the fuel cut for stopping the fuel injection. The fuel cut timing (time point t3) is set relatively late (conversely, the smaller the initial value of N is, the faster it is set). FIG. 7 illustrates the timing relationship between such fuel cut (F / C) and fuel pressure increase control in an easy-to-understand manner. As shown in this figure, when the initial value of the F / C start counter N is set to the minimum 0 because the atmospheric pressure is below AP1 (FIG. 6), the start of fuel pressure increase control (time t2) At the same time, fuel cut is executed. In FIG. 7, the fuel cut timing (at the same time as time t2) at this time is expressed as t3 ₍₀₎ .

On the other hand, in the range where the atmospheric pressure is higher than AP1, the initial value of the F / C start counter N is set larger as the atmospheric pressure is higher, and the fuel cut timing is set later accordingly. In particular, when the initial value of the F / C start counter N is 5 at the maximum, the fuel cut timing is substantially the same as the time when the fuel pressure increase control is completed (that is, when the actual fuel pressure reaches the target value FP2). Set to ₍₅₎ . Further, when the initial value of the F / C start counter N is 1-4, the timing of the fuel cut, the initial value of N is set between the timing of the fuel cut when the 0,5, respectively the time t3 _{( 1) to} t3 ₍₄₎ .

(4) Restart Control Next, the specific content of the engine restart control executed by the restart control unit 62 of the ECU 60 will be described with reference to the flowchart of FIG. As will be apparent from the description here, in this embodiment, the restart control unit 62 of the ECU 60 functions as a determination unit that determines the piston stop position of the compression stroke cylinder 2C during the stop, It also functions as an injection control means for injecting fuel at the start.

  When the process shown in the flowchart of FIG. 8 starts, the restart control unit 62 determines whether or not the engine restart condition is satisfied based on various sensor values (step S21). For example, the brake pedal 37 has been released, the accelerator pedal 36 has been depressed, the engine coolant temperature has fallen below a predetermined value, the amount of decrease in the remaining battery capacity has exceeded an allowable value, The stop time (elapsed time after automatic stop) exceeded the upper limit time, the necessity of air conditioner operation occurred (that is, the difference between the cabin temperature and the set temperature of the air conditioner exceeded the allowable value), etc. When at least one of the requirements is satisfied, it is determined that the restart condition is satisfied.

  When it is determined YES in step S21 and it is confirmed that the restart condition is satisfied, the restart control unit 62 determines whether the stop-time compression stroke cylinder 2C stopped in the compression stroke in accordance with the automatic engine stop control described above. The piston stop position is specified based on the crank angle sensor SW2 and the cam angle sensor SW3, and whether or not the specified piston stop position is within the specified range Rx on the bottom dead center side with respect to the reference stop position X shown in FIG. Is determined (step S22). 9 may vary depending on the shape of the engine (displacement, bore / stroke ratio, etc.), the degree of progress of warm-up, etc., for example, before top dead center (BTDC) 90-75 ° CA. It can be set to any position in between. For example, when the reference stop position X is BTDC 90 ° CA, the specific range Rx is a range of BTDC 180 to 90 ° CA.

  When it is determined YES in Step S22 and it is confirmed that the piston stop position of the stop-time compression stroke cylinder 2C is within the specific range Rx, the restart control unit 62 supplies the first fuel to the stop-time compression stroke cylinder 2C. Control is performed to restart the engine by one compression start for injection (step S23). That is, by driving the starter motor 34 and applying rotational force to the crankshaft 7, fuel is injected from the fuel injection valve 15 into the compression stroke cylinder 2 </ b> C at the time of stop and self-ignited, whereby the engine as a whole is first compressed. Combustion is restarted from the first compression that reaches the dead center, and the engine is restarted.

  On the other hand, when it is determined NO in step S22 and it is confirmed that the piston 5 of the stop-time compression stroke cylinder 2C has stopped at the top dead center side with respect to the specific range Rx, the restart control unit 62 Control is performed to restart the engine by two-compression start in which the first fuel is injected into the stop-time intake stroke cylinder 2D that has been stopped in the stroke (step S24). That is, the starter motor 34 is not injected without injecting fuel until the piston 5 of the stop-time compression stroke cylinder 2C reaches the top dead center and then the stop-time intake stroke cylinder 2D reaches the compression stroke. The engine is forced to rotate only by driving. At that time, fuel is injected from the fuel injection valve 15 into the stop-time intake stroke cylinder 2D, and the injected fuel is self-ignited, so that the engine as a whole is burned from the second compression that reaches the second compression top dead center. Restart and restart the engine.

  Here, in the restart control in the present embodiment, as shown in FIG. 8, the one-compression start (S23) and the two-compression start (S24) are selectively used according to the piston stop position of the stop-time compression stroke cylinder 2C. The reason is as follows.

  As described above, the specific range Rx (FIG. 9) in which one compression start is possible is set on the bottom dead center side with respect to a predetermined reference stop position X (for example, any position between BTDC 90 to 75 ° CA). Has been. If the piston 5 of the stop stroke cylinder 2C is stopped in such a specific range Rx near the bottom dead center, the compression allowance (stroke amount to the top dead center) by the piston 5 is relatively large. As the piston 5 rises at the time of starting, the air in the cylinder 2C is sufficiently compressed to increase in temperature and pressure. For this reason, if the first fuel at the time of automatic start is injected into the stop-time compression stroke cylinder 2C (1 compression start), this fuel will reach self-ignition relatively easily in the cylinder 2C and burn.

  On the other hand, if the piston 5 of the stop compression stroke cylinder 2C deviates from the specific range Rx to the top dead center side, the compression allowance by the piston 5 is small, and even if the piston 5 rises to the top dead center, Since the air is not sufficiently heated to a high temperature and pressure, misfire may occur even if fuel is injected into the compression stroke cylinder 2C when stopped. Therefore, in such a case, the engine is restarted by injecting fuel into the stop intake stroke cylinder 2D instead of the stop compression stroke cylinder 2C to cause self-ignition (two compression start).

  In the above-described two-compression start, combustion based on fuel injection cannot be performed until the second compression at which the piston 5 of the intake stroke cylinder 2D at the time of stop reaches the compression top dead center, and the time required for the automatic start of the engine That is, the time from the start of driving of the starter motor 34 to the complete explosion of the engine becomes long. Therefore, when starting the engine automatically, it is preferable to start the engine by one compression start as much as possible.

  Therefore, in the present embodiment, at the time of fuel injection at the first compression in at least one compression start (fuel injection into the compression stroke cylinder 2C at the time of stop), the fuel is injected in a plurality of times. Specifically, in addition to the main injection injected near or at the compression top dead center, a pre-injection that is a preliminary injection prior to the main injection is performed.

  The fuel by the pre-injection is used to reliably cause diffusion combustion (hereinafter referred to as “main combustion”) that occurs mainly after compression top dead center based on main injection. That is, in a stage earlier than the main injection, a small amount of fuel is injected by pre-injection, and the injected fuel is burned after a predetermined ignition delay (hereinafter, this combustion is referred to as “pre-combustion”). Increase the temperature and pressure to promote the subsequent main combustion.

  More specifically, the pre-injection in this embodiment is performed a plurality of times (before the compression top dead center) and within a crank angle range in which the injected fuel is accommodated in the cavity 5a of the piston 5 crown surface ( (For example, any number of times 2 to 5). If this is the same amount of fuel, it is possible to continuously form a rich air-fuel mixture in the cavity 5a by injecting it in multiple pre-injections rather than injecting it in one pre-injection. This is because the ignition delay can be shortened. That is, by making the pre-injection a plurality of times, the injection amount of the pre-injection per time is reduced and the penetration of the spray is weakened. As a result, the ratio of the fuel remaining in the cavity 5a increases, and as a result, the cavity 5a The air-fuel mixture becomes rich, and the ignitability can be effectively improved.

FIG. 10 is a diagram illustrating a mode of fuel injection for the first compression at the time of the first compression start. Here, as an example, pre-injection is executed three times. Specifically, between BTDC 18 to 10 ° CA, fuel of 2 mm ³ is injected three times as a pre-injection (lower waveform Ip), and then more than the pre-injection as the main injection (at least The fuel is injected at a compression top dead center (BTDC 0 ° CA) (more than that for one pre-injection) (lower waveform Im).

  In the upper part of FIG. 10, the state of combustion caused by the fuel injection as described above is illustrated as a change in the heat generation rate. As understood from the upper waveform of FIG. 10, when the pre-injection (Ip) is executed three times, after the final pre-injection is completed, the pre-injection is performed after a predetermined ignition delay time elapses. Pre-combustion (Bp) occurs due to self-ignition of the fuel. This pre-combustion (Bp) occurs before the compression top dead center (BTDC 0 ° CA) and then converges after reaching the peak of the heat generation rate, but the main injection (Im) starts from the compression top dead center. As a result, main combustion (Bm) due to self-ignition of the main injected fuel continues to occur. This main combustion (Bm) starts combustion after a very short ignition delay (diffusion combustion) based on main injection (Im) executed in a state in which the inside of the cylinder is heated to high temperature and pressure by pre-combustion (Bp). .

  As described above, in this embodiment, at the time of restarting the engine, pre-injection (Ip) is performed at least for the compression stroke cylinder 2C at the time of stop, so the in-cylinder temperature and pressure near the compression top dead center are intentionally The self-ignition of the subsequent main injection (Im) can be promoted. As a result, even when the piston stop position of the stop-time compression stroke cylinder 2C slightly approaches the top dead center side, the engine can be reliably restarted by one compression start.

  In addition, in this embodiment, as shown in FIG. 5 and the like, the fuel pressure increase control for increasing the fuel pressure of the fuel injection valve 15 is executed during the engine automatic stop control. Further, atomization of the fuel when fuel injection (pre-injection and main injection) is performed is promoted. As a result, the ignitability of the injected fuel is further enhanced, and the ignition delay time until self-ignition is shortened. As a result, the startability by one-compression start is further improved.

  Of course, even if the fuel pressure is increased, after the engine is completely stopped, the fuel pressure after the increase cannot be maintained and the fuel pressure gradually decreases. However, in this embodiment, when the engine stop time (elapsed time after the engine is completely stopped) exceeds a predetermined time, the restart condition is satisfied (step S21 in FIG. 8). At the time of restart, the fuel pressure is not extremely reduced, and the engine can be restarted without any problem.

  The reference stop position X (FIG. 9), which is the boundary of the specific range Rx, improves the ignitability by executing the fuel pressure increase control as described above and the fuel injection control at restart including pre-injection together. It is set taking into account. That is, when there is no increase in fuel pressure and pre-injection, the reference stop position X must be set to the bottom dead center side from the example of FIG. 9, but ignition is caused by the increase in fuel pressure and pre-injection. By improving the characteristics, it becomes possible to set the reference stop position X to the top dead center side. As a result, the reference stop position X is far away from the bottom dead center, for example, BTDC 90 to 75 ° CA. The position can be set. As a result, the specific range Rx expands to the top dead center side, so that the piston 5 of the compression stroke cylinder 2C at the time of stoppage falls within the specific range Rx with a higher frequency, and an opportunity to perform a quick restart by one compression start Will increase. In particular, in this embodiment, the geometric compression ratio of the engine body 1 is as low as 14 and it is difficult to ensure the ignitability of the fuel. Therefore, the ignitability at the start is improved by increasing the fuel pressure or the like. However, it is particularly effective in increasing the chance of starting one compression.

  FIG. 10 shows a mode of fuel injection of the first compression (fuel injection to the stop-time compression stroke cylinder 2C) performed at the time of 1-compression start, but compression is performed after the stop-time compression stroke cylinder 2C. As with the first compression, it is desirable to execute combustion control based on pre-injection and main injection for the cylinders that reach the stroke (stop intake stroke 2D and stop exhaust stroke cylinder 2B). The ignitability that is most severe when the engine starts automatically is the first compression that reaches the first compression top dead center of the engine as a whole, but at least the second and third compressions are not sufficiently improved in ignitability. Because it is considered. However, the number of pre-injections can be reduced in the second compression and the third compression in which the engine speed has increased to some extent, compared with the first compression.

  Further, the combustion control based on the pre-injection and the main injection as described above is performed not only at the time of 1 compression start in which combustion by fuel injection is resumed from the first compression but also by 2 compression in which combustion by fuel injection is resumed from the second compression. It is desirable to do the same when starting the engine by starting.

(5) Operational effects and the like As described above, in the present embodiment, in a diesel engine having a so-called idle stop function that automatically stops or restarts the engine under a predetermined condition, Adopting a characteristic configuration.

The automatic stop control unit 61 of the ECU (engine control unit) 60 executes fuel pressure increase control for increasing the fuel pressure of the fuel injection valve 15 until the engine is completely stopped when the automatic engine stop condition is satisfied. Then, the fuel cut for stopping the fuel injection from the fuel injection valve 15 is executed. The fuel cut timing is variably set in accordance with the atmospheric pressure detected by the atmospheric pressure sensor SW8. The higher the atmospheric pressure, the later the timing at which the fuel pressure increase control starts. Specifically, when the atmospheric pressure is equal to or lower than AP1 (for example, 75 kPa) shown in FIG. 6, the fuel cut timing is the time t2 when the fuel pressure increase control is started, as shown at time t3 ₍₀₎ in FIG. Set at the same time. On the other hand, when the atmospheric pressure is higher than the AP1, the fuel cut timing is delayed from the start time t2 of the fuel pressure increase control as the atmospheric pressure is higher, as shown in the time points t3 _{(1) to} t3 ₍₅₎ in FIG. Set to timing.

  Then, when the engine is stopped by the fuel cut and then the restart condition is satisfied, the restart control unit 62 of the ECU 60 causes the piston 5 of the stop-time compression stroke cylinder 2C stopped in the compression stroke to move from a predetermined reference stop position X. It is determined whether or not the fuel is within a specific range Rx (FIG. 9) set on the bottom dead center side. If it is within the specific range Rx, the first fuel is supplied from the fuel injection valve 15 to the compression stroke cylinder 2C at the time of stop. Is injected to restart the engine (1 compression start).

  As described above, in the above embodiment, the fuel pressure increase control for increasing the fuel pressure of the fuel injection valve 15 is executed during the period from when the automatic stop condition is satisfied until the engine is completely stopped. When the fuel is injected from the fuel injection valve 15 for starting, the fuel can be atomized by a relatively high fuel pressure, and the ignitability of the fuel can be improved. When the ignitability of the fuel is enhanced, the piston stop position range (specific range Rx) in which one compression start for restarting the engine by fuel injection into the stop compression stroke cylinder 2C can be expanded to the top dead center side. 1 The opportunity of starting compression can be increased to ensure quick startability.

  In addition, since the fuel pressure increase control is executed before the engine is completely stopped, a general mechanical pump (a pump mechanically driven by the engine) is used as the supply pump 43 that supplies fuel to the fuel injection valve 15. However, the fuel pressure can be increased appropriately. In other words, if the fuel pressure is to be increased after the engine is completely stopped, it is necessary to use a special (e.g., electric) supply pump that can operate independently of the engine. If the fuel pressure is increased before stopping, there is no need to use a special supply pump as described above, so the fuel pressure can be increased without fail and the ignitability can be improved. it can.

  In particular, in the above embodiment, since the fuel cut timing in relation to the fuel pressure increase control is set to be slower as the atmospheric pressure is higher, the start of the fuel pressure increase control (target) is increased as the resistance during inertial rotation of the engine is larger. The fuel cut is executed with a delay from the time t2) when the fuel pressure is set to increase, and the fuel pressure of the fuel injection valve 15 can be increased with a margin before the engine is completely stopped.

In other words, when the atmospheric pressure is high, the pressure at the compression top dead center of each cylinder when the engine is rotating by inertia increases, so the resistance applied to the engine increases accordingly, and the period of inertia rotation of the engine (Period from fuel cut to complete engine stop) is shortened. Therefore, in the above embodiment, when the atmospheric pressure is higher than the predetermined value AP1, the fuel cut is executed after the fuel pressure rises to some extent after a lapse of time from the start of the fuel pressure increase control (time point t2). Thus, even in a situation where the period of inertial rotation of the engine is relatively short because the atmospheric pressure is high, the fuel pressure can be increased with a margin, and the fuel pressure can be increased to a predetermined target value (FP2) before the engine completely stops. It can be surely reached. Moreover, the higher the atmospheric pressure is compared to the predetermined value AP1 (that is, the shorter the inertial rotation period), the later the fuel cut timing is set ₍ see time points t3 _{(1) to} t3 _{(5) in} FIG. 7). Since the increase range of the fuel pressure before the fuel cut is performed is ensured, a desired increase range of the fuel pressure can be reliably obtained even if the inertia rotation period is considerably short.

On the other hand, when the atmospheric pressure is equal to or less than the predetermined value AP1, the fuel cut is executed at time t3 ₍₀₎ , which is the same period as the start of fuel pressure increase control (time t2). It is possible to efficiently increase the fuel pressure while suppressing fuel consumption by utilizing the fact that the inertial rotation of the fuel is prolonged.

That is, when the atmospheric pressure is low, the resistance due to the compressed air during inertial rotation of the engine is small, so that the period of inertial rotation of the engine after fuel cut becomes long (the waveform of the imaginary line in the “engine rotation speed” column of FIG. 5) reference). Therefore, in the above embodiment, when the atmospheric pressure is equal to or less than the predetermined value AP1, as shown by the broken line waveform in the “target injection amount” column of FIG. 5 (or as shown as time point t3 _{(0) in} FIG. 7 _). In addition, the fuel cut is executed simultaneously with the start of the fuel pressure increase control. As a result, the fuel cut timing can be advanced as compared with a case where the fuel cut execution is waited for a while after the start of the fuel pressure increase control (when the atmospheric pressure is higher than AP1). Consumption can be avoided and fuel consumption can be improved. Moreover, even if the fuel cut is executed simultaneously with the start of the fuel pressure increase control, the inertial rotation period of the engine is long, so that the fuel pressure can be sufficiently increased using the engine rotational force during that period, and the fuel pressure can be reduced. The target value (FP2) can be reliably reached.

  As described above, according to the above-described embodiment, the fuel pressure can be increased using the inertial rotation period as much as possible when the engine is automatically stopped. Opportunities for quick restart due to compression start can be further increased.

  Further, in the above embodiment, at the time of one compression start in which the engine is restarted by fuel injection into the stop-time compression stroke cylinder 2C after the engine is automatically stopped, for example, as shown in FIG. Main injection (Im) causing the main combustion (Bm) to reach the peak of the heat generation rate after passing, and pre-combustion (Bp) to reach the peak of the heat generation rate before the start of the main injection ) To cause pre-injection (Ip). According to such a configuration, it is possible to further improve the ignitability at the time of one-compression start and further accelerate the engine start.

  That is, a small amount of pre-injected fuel is combusted by self-ignition after a predetermined ignition delay (pre-combustion), and raises the in-cylinder temperature and pressure of the stop compression stroke cylinder 2C. When executed, the injected fuel will soon burn by self-ignition (main combustion). As described above, the ignitability of the fuel injected by the main injection is improved by the pre-injection (pre-combustion) before that, so that the compression allowance (stroke amount to the top dead center) in the compression stroke cylinder 2C at the time of stop is so much. Even if not, combustion in the compression stroke cylinder 2C at the time of stop is reliably performed. As a result, the piston stop position range (specific range Rx) in which one compression start is possible can be expanded to the top dead center side, and the engine start can be further accelerated.

  Furthermore, in the above embodiment, since the pre-injection is executed a plurality of times at a timing such that the fuel is contained in the cavity 5a provided on the crown surface of the piston 5, it is easy to ignite the inside of the cavity 5a (ignition delay time). (Short) can be reliably formed. As a result, the pre-injected fuel is self-ignited more reliably (pre-combustion), which promotes self-ignition (main combustion) of the main-injected fuel. Can be increased.

  In particular, in the configuration of the above embodiment in which the fuel pressure is increased in advance before the fuel cut, when the number of pre-injections is set to one, a relatively large amount of fuel is injected at a high fuel pressure by the pre-injection, The penetration of the spray becomes stronger, and the tendency of the injected fuel to diffuse to the outside of the cavity 5a becomes stronger. Then, the ratio of the rich air-fuel mixture formed in the cavity 5a is lowered, and there is a possibility that the ignitability is deteriorated. On the other hand, when the number of pre-injections is set to a plurality of times as in the above embodiment, the amount of injection per pre-injection is reduced and the penetration is weakened. A mixture can be formed, and the ignitability of the fuel can be effectively enhanced.

  In the above embodiment, the automatic stop control unit 61 (fuel pressure adjusting means) of the ECU 60 removes all the SCVs 43b built in the supply pump 43 from when the automatic stop condition is satisfied until the fuel cut is executed. Although the control for closing is executed, and thereby the fuel pressure of the fuel injection valve 15 is increased, the control of the fuel pressure adjusting means in the present invention only needs to be able to increase the fuel pressure with a response not so slow, It is not particularly limited to the control using the SCV 43b.

In the above embodiment, as shown in FIG. 7, when the atmospheric pressure detected by the atmospheric pressure sensor SW8 is equal to or less than the predetermined value AP1 (when the initial value of the F / C start counter N is 0), Although the fuel cut timing is set at time t3 ₍₀₎ , which is the same time as the start of fuel pressure increase control (time t2), it is not always necessary to be at the same time as the start of fuel pressure increase control. For example, the fuel cut may be executed slightly earlier than the time point t2 at which the fuel pressure starts to rise.

Conversely, as shown in FIG. 11, the fuel cut timing when the atmospheric pressure is less than or equal to the predetermined value AP1 is set to a time point t3 ′ ₍₀₎ slightly delayed from the start of the fuel pressure increase control (time point t2). Also good. However, it is necessary to set the fuel cut timing when the atmospheric pressure is equal to or less than the predetermined value AP1 earlier than the point in time when the fuel pressure reaches the target value FP2 (point of arrow Z). This is because the fuel pressure is increased by using the force of the engine during inertial rotation even if the atmospheric pressure is low and the inertial rotation period of the engine is long.

On the other hand, the fuel cut timing when the atmospheric pressure is higher than the predetermined value AP1 (when the initial value of the F / C start counter N is 1 or more) is the time t3 _{(1) to} t3 ₍₅₎ in FIG. As is apparent from time point t3 ′ _{(1) of} 11, it is always set later than the start of fuel pressure increase control (time point t2). This is because it is necessary to raise the fuel pressure as much as possible before the fuel cut is performed under conditions where the atmospheric pressure is high and the inertial rotation period of the engine is short.

  Moreover, in the said embodiment, although the preferable form of this invention was demonstrated taking the example of the diesel engine provided with the engine main body 1 whose geometric compression ratio is 14, the engine which can apply the structure of this invention naturally. Is not limited to a geometric compression ratio of 14. For example, a diesel engine having a geometric compression ratio of less than 16 has a lower compression ratio and a relatively poor ignitability compared to conventionally used diesel engines. There is room for suitably applying the configuration of the present invention to improve the ignitability. On the other hand, it is considered that the geometric compression ratio of the diesel engine is required to be 12 or more from the limit of ignitability. From the above, the diesel engine to which the present invention can be suitably applied is a diesel engine having a geometric compression ratio of 12 or more and less than 16, more preferably a diesel engine having a geometric compression ratio of 13 or more and 15 or less. You can say that.

  In the above embodiment, the preferred embodiment of the present invention has been described by taking the AT vehicle in which the crankshaft 7 of the engine body 1 is connected to the automatic transmission 101 via the torque converter 102 as an example. Can be applied not only to AT vehicles but also to MT vehicles in which the crankshaft is connected to a manual transmission via a clutch. However, in the MT vehicle, a flywheel having a relatively large mass is attached to one end of the crankshaft. Therefore, due to the inertia of the flywheel, the period during which the engine rotates by inertia after the fuel cut is longer than that of the AT vehicle. For this reason, it is considered that it is not always necessary to employ a configuration in which the fuel cut timing is variably set according to the atmospheric pressure as in the present invention.

  That is, in an MT vehicle having a long inertial rotation period of the engine, the fuel cut timing can be uniformly set at the same time as the start of the fuel pressure increase control regardless of the atmospheric pressure. On the other hand, in the AT car, the period of inertial rotation of the engine is relatively short. Therefore, if the timing of fuel cut is set uniformly at the same time as the start of fuel pressure increase control (time t2 in FIGS. 5 and 7). In particular, when the atmospheric pressure is high, the period during which the engine rotates by inertia becomes considerably short, and the fuel pressure may not be raised to the target value during the inertia rotation. Therefore, it can be said that the configuration of the present invention in which the timing of fuel cut is delayed when the atmospheric pressure is high is more meaningful when applied to an AT vehicle than to an MT vehicle.

  In the above embodiment, the fuel cut timing is variably set according to the atmospheric pressure value detected by the atmospheric pressure sensor SW8 (detection means). However, in order to determine the fuel cut timing. These parameters are not necessarily limited to atmospheric pressure. The resistance applied to the engine during the inertial rotation of the engine is directly affected by the pressure at the compression top dead center of each cylinder. Therefore, the higher the compression top dead center pressure, the longer the inertial rotation period of the engine. (The lower the pressure, the shorter the inertial rotation period). Therefore, the parameter for determining the fuel cut timing may be any physical quantity proportional to the compression top dead center pressure during inertial rotation. In the above embodiment, the atmospheric pressure is detected as the parameter using the fact that the atmospheric pressure is proportional to the compression top dead center pressure during inertial rotation. For example, an in-cylinder pressure sensor that detects in-cylinder pressure. The compression top dead center pressure during inertial rotation may be directly detected by the in-cylinder pressure sensor.

  In the above-described embodiment, in the automatic engine stop control, when the automatic stop condition is satisfied, the opening degree of the intake throttle valve 30 is reduced to the fully closed state (0%), and is kept fully closed until the engine is completely stopped. However, in order to make the piston stop position of the compression stroke cylinder 2C at the time of stop fall within the specific range Rx (lower dead center side than the reference stop position X) with a higher probability, the following intake throttle valve 30 is used. It is also conceivable to perform the opening degree control.

  Specifically, in order to increase the probability that the piston stop position of the stop-time compression stroke cylinder 2C falls within the specific range Rx, the top dead center of the engine immediately before the final TDC (time point t4 in FIG. 5) after the fuel cut is performed. When the passage timing is reached, the intake throttle valve 30 may be driven in the opening direction to increase the opening to a predetermined opening (for example, about 10 to 30%). In this way, in other words, the cylinder in which the intake air flow rate to the compression stroke cylinder 2C at the time of stoppage that reaches the intake stroke from the top dead center one before the final TDC is the intake stroke from the top dead center two times before the final TDC, Then, when the engine is completely stopped, the intake air flow rate increases with respect to the expansion stroke cylinder at the time of stop (first cylinder 2A in FIG. 5) in the expansion stroke. When the difference in intake flow rate occurs in this way, the piston stop position of the compression stroke cylinder 2C at the time of stoppage is naturally close to the bottom dead center due to the unbalance of the force that the compressed air tries to push down the piston 5 (the expansion stroke at the time of stoppage). Since the piston stop position of the cylinder 2A is close to the top dead center), the piston 5 of the stop-time compression stroke cylinder 2C is stopped in the specific range Rx on the bottom dead center side with respect to the reference stop position X with a fairly high probability. Will be able to.

  The present invention is not limited to a diesel engine (an engine that burns light oil by self-ignition) as in the above embodiment as long as it is a compression self-ignition engine. For example, recently, an engine of a type that compresses fuel containing gasoline at a high compression ratio and self-ignites has been researched and developed, but the present invention also applies to such a compression self-ignition type gasoline engine. Such automatic stop / restart control can be suitably applied.

DESCRIPTION OF SYMBOLS 1 Engine main body 2A-2D Cylinder 5 Piston 5a Cavity 15 Fuel injection valve 34 Starter motor 43 Supply pump 61 Automatic stop control part (fuel cut control means, fuel pressure adjustment means)
62 Restart control unit (determination means, injection control means)
101 automatic transmission 102 torque converter SW7 atmospheric pressure sensor (detection means)
X Reference stop position Rx Specific range Ip Pre-injection Im Main injection Bp Pre-combustion Ip Main combustion

Claims (6)

Provided in a vehicle equipped with a compression self-ignition engine that burns fuel injected from the fuel injection valve into the cylinder by self-ignition, and automatically stops the engine when a predetermined automatic stop condition is satisfied, and then When the restart condition is satisfied, a start control device that restarts the engine by injecting fuel from the fuel injection valve while applying a rotational force to the engine using a starter motor,
Fuel cut control means for executing a fuel cut to stop fuel injection from the fuel injection valve when the automatic stop condition is satisfied;
Detecting means for detecting a predetermined parameter proportional to the compression top dead center pressure in the cylinder when the engine rotates by inertia after the fuel cut;
As the fuel pressure in the upper Symbol fuel injection valve during a period from the automatic stop condition is satisfied until the engine stops completely rises to a predetermined target value, the fuel pressure increases at a predetermined timing after establishment of the automatic stop condition Fuel pressure adjusting means for starting control;
Determination means for determining whether or not the piston of the compression stroke cylinder at the time of stoppage in the compression stroke when the engine is completely stopped is in a specific range set on the bottom dead center side with respect to a predetermined reference stop position;
When it is determined that the piston of the stop compression stroke cylinder has stopped within the specific range and the engine restart condition is satisfied, the fuel injection valve is controlled to control the first fuel in the stop compression stroke cylinder. Injection control means for injecting
The fuel injection valve receives fuel from a supply pump mechanically driven by an engine.
The fuel cut control means variably sets the fuel cut timing in relation to the fuel pressure increase control according to the value of the parameter detected by the detection means,
The fuel cut timing set by the fuel cut control means is set to a timing later than the start point of the fuel pressure increase control when the parameter is higher than a predetermined value, while the parameter When the fuel pressure is lower than the predetermined value, the compression self is set earlier than the fuel cut timing when the fuel pressure is higher than the predetermined value and earlier than the fuel pressure rises to the target value. Ignition engine start control device. The start control device for a compression self-ignition engine according to claim 1,
When the parameter is higher than the predetermined value, the fuel cut timing set by the fuel cut control means is set to be slower as the parameter is higher within a range later than the start time of the fuel pressure increase control. On the other hand, when the parameter is equal to or less than the predetermined value, the compression self-ignition engine start control device is set at the same time as the start of the fuel pressure increase control. The start control device for a compression self-ignition engine according to claim 1 or 2,
A start control device for a compression self-ignition engine, wherein the parameter detected by the detection means is atmospheric pressure. The start-up control device for a compression self-ignition engine according to any one of claims 1 to 3,
After the restart condition is satisfied, the injection control means causes main combustion that reaches the peak of the heat generation rate after passing the compression top dead center at least as the first fuel injection to the compression stroke cylinder at the time of stop. A start control device for a compression self-ignition engine, wherein the main injection to be performed and pre-injection that causes pre-combustion to reach a peak of the heat generation rate before the start of the main injection are executed. The start-up control device for a compression self-ignition engine according to any one of claims 1 to 4,
The compression self-ignition engine is a diesel engine having a geometric compression ratio set to less than 16 and a start-up control device for a compression self-ignition engine. The start-up control device for a compression self-ignition engine according to any one of claims 1 to 5,
A compression self-ignition engine start control device, wherein the crankshaft of the compression self-ignition engine is connected to an automatic transmission through a torque converter.

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